放棄Ceph，Salesforce使用 Apache BookKeeper 在雲中實現最強存儲

{"type":"doc","content":[{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"本文要點"}]},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"使存儲系統感知雲的傳統方式是直接遷移，這種方式表現良好，但從我們的經驗來看，重構雲感知架構效果更好。"}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"目前，在跨區域環境中部署 Apache BookKeeper 時需要手動將存儲節點映射到特定區域\/可用性區域，但在區域中斷時，持久性和可用性會受到影響。"}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"Salesforce 獨有的使 Apache BookKeeper 感知雲的方法是通過智能化存儲節點，讓其在雲中部署可以有效運轉，並保證持久性和可用性。"}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"這些方法簡化了集羣的改進、升級和重啓操作，對消費服務的影響最低。"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"在 Salesforce，我們需要可以同時處理兩種流的存儲系統：一種流用來預寫日誌，另一種流用來處理數據。但對這兩種流，我們的要求相互矛盾：預寫日誌流的寫入延遲低，而讀取吞吐量高；數據流的寫入吞吐量高，但隨機讀取延遲低。作爲雲計算的領軍企業，我們的存儲系統必須具備雲感知能力（可用性和持久性要求越來越高）。爲了在商用硬件上運行並方便擴容，我們無法更改部署模型設計。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"開源方案"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"在對存儲系統進行初步研究後，我們考慮是自己搭建一套還是購買一套。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"考慮到整體規劃和上市時間、資源、成本等主要的業務驅動因素，我們決定使用開源存儲系統。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"在查看了開源代碼後，我們有兩個備選方案：Ceph 和 Apache BookKeeper。由於這套系統需要對客戶開放，可擴展性和一致性都很重要，系統必須完全滿足用例的 CAP（Consistency：一致性；Availability：可用性；Partition Tolerance：分區容錯性）要求以及我們自己的特殊需求。首先，我們來看一下 BookKeeper 和 Ceph 在 CAP 和其他方面的表現。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"Ceph 可以保證一致性和分區容錯，讀取路徑可以藉助不可靠讀取提供可用性和分區容錯；但要使寫入路徑保證可用性和分區容錯性並不容易。並且，我們不能更改部署數據。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"我們決定選擇 Apache BookKeeper。BookKeeper 支持僅追加\/不可變數據存儲，採用高可複製的分佈式日誌，滿足我們對系統 CAP 的要求。BookKeeper 還具備以下特點："}]},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"已 Ack 的寫入始終可讀。"}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"已讀 Entry 始終可讀。"}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"無 Master 服務器，客戶端使用 Apache ZooKeeper 實現共識（consensus）算法，獲取元數據。"}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"數據佈局無需複雜的哈希\/計算。"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"Salesforce 也一直支持"},{"type":"link","attrs":{"href":"https:\/\/opensource.salesforce.com\/","title":null,"type":null},"content":[{"type":"text","marks":[{"type":"underline"}],"text":"開源"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"產品，Apache BookKeeper 社區積極活躍，充滿活力。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"Apache BookKeeper——近乎完美，但還有改善空間"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"Apache BookKeeper 幾乎實現了我們對存儲系統的全部要求，但仍需做一些工作。首先來看一下 Apache BookKeeper 可以實現我們的哪些要求。"}]},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"存儲節點稱爲 Bookie；一組 Bookie 稱爲 Ensemble。"}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"寫入的最小單元爲 Entry，Entry 不可更改。"}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"一組 Entry 稱爲 Ledger，Ledger 僅可追加，不可更改。"}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"寫入或複製 Bookie 的數量稱爲 Write Quorum——Entry 的最大副本數。"}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"確認寫入前 Bookie 的數量稱爲 Ack quorum——Entry 的最小副本數。"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"從持久性來看，Ledger 跨 Bookie Ensemble 複製，Ledger 內的 Entry 可以跨 Ensemble。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https:\/\/res.infoq.com\/articles\/storage-cloud-apache-bookkeeper\/en\/resources\/60image001-1619467931640.jpg","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":"center","origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}},{"type":"strong"}],"text":"Ensemble Size: 5 Write Quorum Size: 3 Ack Quorum Size: 2"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"寫入根據 Write Quorum 和 Ack Quorum（可配置）進行確認，從而保證低寫入延遲和高可擴展。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"但實際上，在雲中的商用硬件上運行 BookKeeper 並不輕鬆。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"數據佈局策略不具備雲感知能力，並且沒有顧及底層雲服務提供商（雲基礎設施）。目前，一些用戶的部署方法是手動標識不同可用性區域中的節點，並進行邏輯分組，然後以組爲單位改進數據佈局策略。這不失爲一種解決方案，但不支持區域故障，也降低了維護和升級大型集羣時系統的易用性。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"另外，所有云基礎設施的可用區域裏都出現過停機情況；而一般的理解是，應用程序要針對這些故障做相應的設計。一個很好的例子是，"},{"type":"link","attrs":{"href":"https:\/\/netflixtechblog.com\/post-mortem-of-october-22-2012-aws-degradation-efcee3ab40d5","title":null,"type":null},"content":[{"type":"text","text":"2012 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網絡服務"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"link","attrs":{"href":"https:\/\/netflixtechblog.com\/post-mortem-of-october-22-2012-aws-degradation-efcee3ab40d5","title":null,"type":null},"content":[{"type":"text","text":"可用區域故障"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"link","attrs":{"href":"https:\/\/netflixtechblog.com\/post-mortem-of-october-22-2012-aws-degradation-efcee3ab40d5","title":null,"type":null},"content":[{"type":"text","text":"，Netflix"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"link","attrs":{"href":"https:\/\/netflixtechblog.com\/post-mortem-of-october-22-2012-aws-degradation-efcee3ab40d5","title":null,"type":null},"content":[{"type":"text","text":"底層"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"link","attrs":{"href":"https:\/\/netflixtechblog.com\/post-mortem-of-october-22-2012-aws-degradation-efcee3ab40d5","title":null,"type":null},"content":[{"type":"text","text":"所依賴的公有云"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"link","attrs":{"href":"https:\/\/netflixtechblog.com\/post-mortem-of-october-22-2012-aws-degradation-efcee3ab40d5","title":null,"type":null},"content":[{"type":"text","text":"基礎設施"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"link","attrs":{"href":"https:\/\/netflixtechblog.com\/post-mortem-of-october-22-2012-aws-degradation-efcee3ab40d5","title":null,"type":null},"content":[{"type":"text","text":"停機，"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"link","attrs":{"href":"https:\/\/netflixtechblog.com\/post-mortem-of-october-22-2012-aws-degradation-efcee3ab40d5","title":null,"type":null},"content":[{"type":"text","text":"而"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"link","attrs":{"href":"https:\/\/netflixtechblog.com\/post-mortem-of-october-22-2012-aws-degradation-efcee3ab40d5","title":null,"type":null},"content":[{"type":"text","text":"Netflix 服務仍然可以在"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"link","attrs":{"href":"https:\/\/netflixtechblog.com\/post-mortem-of-october-22-2012-aws-degradation-efcee3ab40d5","title":null,"type":null},"content":[{"type":"text","text":"有限的容量上"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"link","attrs":{"href":"https:\/\/netflixtechblog.com\/post-mortem-of-october-22-2012-aws-degradation-efcee3ab40d5","title":null,"type":null},"content":[{"type":"text","text":"運行"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"公有云中的問題"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"公有云基礎設施易於擴展，在一定程度上降低了使用和維護的成本，因此，從網站到應用程序，甚至是企業級軟件，基本都在公有云服務提供商提供的基礎設施上運行。但是，公有云也有其缺陷，它在節點、區域或地區層面都可能出現不可用的情況。底層基礎設施不可用，用戶什麼都做不了。起因可能是某些機器、區域或地區出現故障，也可能是由硬件故障引起的網絡延遲增加。所以最終當在公有云基礎設施上運行應用程序時，開發人員在設計時需要考慮由故障引發的問題。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"Apache BookKeeper 本身不能解決這一問題，因此，我們需要自行設計一個修復程序。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"Salesforce 重構"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"對問題有了一定的瞭解之後，我們開始考慮解決方案，讓 BookKeeper 具備雲感知能力，滿足我們的以下要求。"}]},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"在公有云集羣中的 Bookie 需要一個標識。"}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"根據可用區域內 Ensemble 的分佈設計數據佈局策略，實現更好的高可用，簡化維護和部署。"}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"改進 Bookie 已有的功能，如讀取、寫入、數據複製等，使 Bookie 可以充分利用多區域佈局的優勢，並計算跨區域傳輸數據的成本。"}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"上述工作和雲基礎設施無關。"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"我們的解決方案如下。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"雲感知能力：Cookie 和 Kubernetes"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"現有的 BookKeeper 架構爲所有 Bookie 提供唯一標識（在首次啓動時分配）。標識存儲在元數據存儲（ZooKeeper）中，其他 Bookie 或客戶端可以訪問。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"使 Apache BookKeeper 具有云感知能力的第一步是讓所有 Bookie 均可獲取它部署在 Kubernetes 集羣中的位置。 我們認爲 Cookie 數據是獲取位置信息的最佳方式。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"因此，我們在 Cookie 中增加了 networkLocation 字段，它包含兩部分：可用區域和升級域，用於定位 Bookie。Kubernetes 和雲基礎設施無關，我們可以使用 Kubernetes API 來查詢底層的可用區域信息。我們還根據涉及主機名順序索引的公式生成了 upgradeDomain 字段。它可以用來滾動升級，而不影響集羣的可用性。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"在機器啓動時生成上述字段和對應值，並保存在元數據存儲中供用戶訪問。這些信息可以用於生成 Ensemble，分配 Bookie 到 Ensemble，以及確定從哪些 Bookie 複製數據，複製的數據存儲到哪些 Bookie。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https:\/\/res.infoq.com\/articles\/storage-cloud-apache-bookkeeper\/en\/resources\/51image003-1619469338598.jpg","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"公有云佈局策略"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"現在，客戶端已經足夠智能，可以與某些區域中的 Bookie 進行通信，下一步便是確保有一個可以使用這一信息的數據佈局策略。我們開發了 ZoneAwareEnsemblePlacementPolicy（ZEPP）。這是一個針對基於雲部署而設計的兩級層次化佈局策略。ZEPP 可以獲取可用區（AZ）和 upgradeDomains（UD）信息。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"AZ 是區域內隔離數據中心的邏輯概念；UD 是 AZ 內的一組節點，關閉 UD 不會影響服務，UD 還可以監測到區域的關閉和重啓。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"下圖爲 ZEPP 可採用的一種部署示意圖。這種部署方式兼顧了 Cookie 中的 AZ 和 UD 信息，並據此對 Bookie 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可以具備雲感知能力了。但成本也是設計架構時必須考慮的因素之一。大多數雲基礎設施對傳出服務的數據進行單向收費，跨可用區傳輸的費用會有所不同。這是 BookKeeper 客戶端需要考慮的一個重要因素，因爲它現在是從 Ensemble 中隨機選擇一個 Bookie 進行讀取。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"如果 Bookie 和客戶端屬於不同的可用區，會增加不必要的成本。數據複製可能發生在跨可用區的 Bookie 之間，當可用區出現故障時，使用成本會增加。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"我們通過以下方式來處理這些特殊情況。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"重排序讀取"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"目前，BookKeeper 客戶端從 Ensemble 隨機選取 Bookie 進行讀取。藉助重排序讀取特性，現在客戶端可以選擇 Bookie，從而減小讀延遲，降低成本。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"啓用重排序讀取後，客戶端按照以下順序選擇 Bookie："}]},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"本地區域中滿足要求且待處理請求少的 Bookie；"}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"遠程區域中滿足要求且待處理請求少的 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要求，引起“"},{"type":"link","attrs":{"href":"https:\/\/zh.wikipedia.org\/wiki\/%E6%83%8A%E7%BE%A4%E9%97%AE%E9%A2%98","title":null,"type":null},"content":[{"type":"text","marks":[{"type":"underline"}],"text":"驚羣問題"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"”。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"要解決這一問題，首先要確定區域關閉的時間。故障可能是暫時性的操作失誤，比如網絡故障引起區域不可用，我們不希望系統複製 TB 級的數據；但同時我們也要做好準備，應對真正的故障。我們的解決方案包含兩步："}]},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"辨別區域是真正故障還是暫時故障；"}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"將整個區域的大規模自動複製轉換爲手動操作。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":"br"}}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"下圖爲區域關閉與重啓時我們的應對方案。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https:\/\/res.infoq.com\/articles\/storage-cloud-apache-bookkeeper\/en\/resources\/33image007-1619467931640.jpg","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":"根據區域中可用 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Anup（"},{"type":"link","attrs":{"href":"https:\/\/twitter.com\/ghatageanup","title":null,"type":null},"content":[{"type":"text","marks":[{"type":"underline"}],"text":"@ghatageanup"}],"marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#494949","name":"user"}}],"text":" 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